Tiltwing multicopter with foldable and non-foldable propellers

ABSTRACT

An aircraft includes a tiltwing where the tiltwing is a single wing to which starboard-side and non-foldable outer propeller, a port-side and non-foldable outer propeller, a starboard-side and foldable inner propeller, and a port-side and foldable inner propeller are coupled to. Those rotors rotate at least some of the time when the tiltwing is in a vertical takeoff and landing position. The starboard-side and foldable inner propeller and the port-side and foldable inner propeller are stowed at least some of the time when the tiltwing is in a forward flight position. The tiltwing rotates about an axis of rotation, when rotating between the vertical takeoff and landing position and the forward flight position, that is higher than the aircraft&#39;s center of mass.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 15/801,052 entitled TILTWING MULTICOPTER WITH FOLDABLE ANDNON-FOLDABLE PROPELLERS filed Nov. 1, 2017 which is incorporated hereinby reference for all purposes.

BACKGROUND OF THE INVENTION

Although new types of aircraft are being developed which areall-electric, further improvements are always desirable. For example,new types of aircraft which improve upon the aircraft's responsiveness,stability, and/or range performance would be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a diagram showing an elevated view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding.

FIG. 2 is a diagram showing a side view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding.

FIG. 3 is a diagram illustrating a front view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding.

FIG. 4 is a diagram illustrating a top view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding.

FIG. 5 is a diagram showing an elevated view of an embodiment of amulticopter with its tiltwings in a position for forward flight.

FIG. 6 is a diagram showing a side view of an embodiment of amulticopter with its tiltwings in a position for forward flight.

FIG. 7 is a diagram illustrating a front view of an embodiment of amulticopter with its tiltwings in a position for forward flight.

FIG. 8 is a diagram illustrating a top view of an embodiment of amulticopter with its tiltwings in a position for forward flight.

FIG. 9 is a diagram illustrating an embodiment of a transition fromvertical takeoff to forward flight.

FIG. 10 is a flowchart of a transitional process from a vertical takeoffand landing position to a forward flight position.

FIG. 11 is a flowchart of a transitional process from a forward flightposition to a vertical takeoff and landing position.

FIG. 12A is a diagram illustrating an embodiment of actuation cylinderswhich are used to rotate the front tiltwing and back tiltwing where thetiltwings are in a vertical takeoff and landing position.

FIG. 12B is a diagram illustrating an embodiment of actuation cylinderswhich are used to rotate the front tiltwing and back tiltwing where thetiltwings are in a forward flight position.

FIG. 13A is a front-view diagram illustrating an embodiment of afoldable propeller with extended blades.

FIG. 13B is a front-view diagram illustrating an embodiment of afoldable propeller with folded blades.

FIG. 14A is a side-view diagram illustrating an embodiment of a foldablepropeller with extended blades.

FIG. 14B is a side-view diagram illustrating an embodiment of a foldablepropeller with folded blades.

FIG. 15A is a top-view diagram illustrating an embodiment of a foldablepropeller with extended blades.

FIG. 15B is a top-view diagram illustrating an embodiment of a foldablepropeller with folded blades.

FIG. 16A is an angled-view diagram illustrating an embodiment of afoldable propeller with extended blades.

FIG. 16B is an angled-view diagram illustrating an embodiment of afoldable propeller with folded blades.

FIG. 17A is a diagram illustrating an embodiment of foldable propellerwith open blades and a pylon shaped to fit the stowed blades.

FIG. 17B is a diagram illustrating an embodiment of foldable propellerwith folded blades and a pylon shaped to fit the stowed blades.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

Various embodiments of a tiltwing multicopter are described herein. Insome embodiments, the aircraft includes a front tiltwing (where thefront tiltwing includes two non-foldable outer propellers and fourfoldable inner propellers, the four foldable inner propellers arerotating at least some of the time while the front tiltwing is held in avertical takeoff and landing position, and the four foldable innerpropellers are stowed at least some of the time while the front tiltwingis held in a forward flight position) and a back tiltwing which includestwo non-foldable back propellers. First, various views of an exemplarymulticopter in a vertical takeoff and landing position are described.Then, various views of the multicopter in a forward flight position aredescribed.

FIG. 1 is a diagram showing an elevated view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding. In the example shown, the multicopter is capable of taking offand landing in a vertical manner. This may be desirable, for example,when there is a limited amount of space to take off or land.

The aircraft has two tiltwings: a front tiltwing (100) with sixpropellers (sometimes referred to as rotors) and a back tiltwing (102)with two propellers. In this example, the outer propellers (104) whichare attached to the front tiltwing (100) are not foldable whereas theinner propellers (106) on that tiltwing are foldable. Vertical takeoffand landing requires greater thrust than that for forward flight, and soall of the propellers are shown in their open position and are in usehere. As will be described in more detail below, the foldable innerpropellers (106) are put into a closed or folded position during forwardflight since the additional thrust from those propellers is not neededduring forward flight. Turning off those propellers conserves batterylife and increases range (the exemplary aircraft is an all-electricaircraft) and closing those propellers reduces drag.

The example multicopter shown here has the following overall dimensions:

TABLE 1 Overall Dimensions Span of Front Tiltwing ~7 meters (~23 feet)Span of Back Tiltwing 2 meters (~6.6 feet) Nose-to-Tail Length 5 meters(~16.4 feet)In this example, the dimensions of the multicopter are selected so thatthe multicopter can fit into a trailer and be towed. For example, manystates permit trailers with maximum widths of 8 feet and 6 inches. Thedimensions of the multicopter permit the multicopter to fit (e.g.,sideways) into a trailer and be towed.

In some embodiments, the exemplary multicopter is an ultralightaircraft, for example, as specified and/or regulated by the FederalAviation Administration in the United States, the Civil AviationAuthority in New Zealand, etc. Such ultralight aircraft often weighs onthe order of hundreds of kilograms. In this example, the multicoptershown has a gross weight of ˜330 kg.

The front tiltwing (100) in this example is a straight, prismatic wing.A straight, prismatic wing is lighter and easier to manufacture thansome other types of wings, such as a swept back wing. A straight,prismatic wing also has lower drag than a swept back wing. For thesereasons, a straight, prismatic wing was selected for this design.

The back tiltwing (102) in this example includes two verticalstabilizers (110) connected to a horizontal stabilizer (112); thisconfiguration is sometimes referred to as an H tail or a twin tail. Thevertical tail area associated with the vertical stabilizers gives themulticopter good yaw stability. This tail arrangement with two verticalstabilizers is also more attractive than a tail with a single, tallervertical stabilizer since the same surface area (and correspondingly,degree of yaw stability) can be achieved while achieving a lowermulticopter height (e.g., which makes it easier to put the multicopterinto a trailer).

Compared to a previous prototype, the version shown here has a longerfuselage, for example approximately 5 meters from nose to tail comparedto the previous length of approximately 3.5 meters from nose to tail.The previous prototype also did not include a twin tail. Rather, theprevious prototype had a single canard (i.e., a single verticalstabilizer). Both of these things enable the current version shown hereto have more yaw stability over the previous prototype.

The back tiltwing (102) includes two non-foldable propellers (108);sometimes these propellers are called the non-foldable back propellersin order to differentiate them from the non-foldable outer propellers(104) on the front tiltwing (100). By including propellers on the backtiltwing, the multicopter has additional lift, which is especiallydesirable during vertical takeoff and landing.

All of the propellers are connected to their respective tiltwing on theleading edge of the blade via a pylon. In the case of the foldable innerpropellers (106) attached to the front tiltwing, the pylons providesufficient clearance so that the blades of the propellers can be foldedand/or stowed away without the tips of the blades coming into contactwith the leading edge of the front tiltwing. For the non-foldable outerpropellers (104), the pylons are slightly lower than the pylons for thefoldable inner propellers, but some clearance between the leading edgeof the front tiltwing and those propellers is desirable so that the tipof the blade does not hit the tiltwing. In this example, the propellershave dimensions in the following ranges. In the below table, the pylonclearance dimension refers to the distance between the plane of rotationassociated with a particular group of propellers and the (e.g., leadingedge of the) tiltwing to which that group of propellers is attached. Thepylon clearance dimension does not, for example, include the height ofany cap on the propeller.

TABLE 2 Propeller Dimensions Group of Propellers Diameter Range PylonClearance Range Non-Foldable Propellers 0.5-1 meters Not ApplicableFoldable Propellers 1-1.5 meters 1-10 cm

Since the foldable inner propellers (106) are primarily used forvertical takeoff and landing, those propellers may be optimized for thattype of use. For example, the blade characteristics (e.g., twist angle,pitch angle, etc.) may be optimized for vertical thrust and/or verticallift. With respect to pitch angle, presenting a flatter blade to therelative wind is better for this type of flight. A flatter pitch angleprovides more upward thrust and therefore is good for vertical takeoffand landing where a lot of upward thrust is desired. Also, the twistangle may be selected and/or optimized for vertical takeoff and landing(e.g., the blade tip has a twist angle of 10-20 degrees, which is goodfor vertical takeoff and landing).

The following figure shows a corresponding side view.

FIG. 2 is a diagram showing a side view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding. In the example shown, the multicopter's center of mass (200) isshown. It is noted that the center of mass is dependent upon theposition of the tiltwings and the center of mass may change when thefront tiltwing (202) and back tiltwing (204) change positions (e.g., thetiltwings rotate to be in a forward flight position). The front tiltwinglift vector (206) and the back tiltwing lift vector (208) are also shownand as this side view shows, the center of mass (200) is located betweenthe two lift vectors (206 and 208). This relative positioning (i.e.,with the center of mass between the two lift vectors) makes themulticopter easier to maneuver and/or more stable in this position.

This view also shows the two hinges about which the tiltwings rotatewhen switching between the vertical takeoff and landing position (shown)and the forward flight position (not shown). Hinge 210 shows the hingeabout which the front tiltwing (202) rotates and hinge 212 shows thehinge about which the back tiltwing (204) rotates. It is noted that thecenter of mass (200) is lower than both the front tiltwing hinge (210)and the back tiltwing hinge (212). This arrangement is desirable withrespect to layout and parts placement. In some embodiments, the hingesare corner hinges (e.g., door hinges) where a first plate or surface isconnected to the fuselage and a second plate or surface is connected tothe appropriate tiltwing.

The following figure shows a corresponding front view.

FIG. 3 is a diagram illustrating a front view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding. From the view shown, different pylon heights associated withthe front tiltwing (300) are more apparent. The two non-foldable outerpropellers (302) have a shorter pylon whereas the four foldable innerpropellers (304) are attached to the front tiltwing (300) using tallerpylons. Although partially obscured, the back tiltwing (306) and backtiltwing propellers (308) are identified for context.

This view of the multicopter also shows that the front tiltwing (300)includes a cutout (310). As will be described in more detail below, whenthe front tiltwing rotates down and/or forward into the forward flightposition, the cutout will fit neatly with the top of the fuselage.

The following figure shows a corresponding top view.

FIG. 4 is a diagram illustrating a top view of an embodiment of amulticopter with its tiltwings in a position for vertical takeoff andlanding. From this top view, the relative diameters of the variouspropellers are more apparent. As described above in Table 2, thediameter of the non-foldable back propellers (400), which are attachedto the back tiltwing (402), and the non-foldable outer propellers (404),which are attached to the front tiltwing (406), are smaller in diametercompared to the foldable inner propellers (408). The cruise propellersmust have steeper pitches such that they are able to provide thrust incruise, while the folding propellers are shallow pitch and able togenerate thrust more capably in hover. A shallower pitch blade at largediameters is more efficient and uses less torque per thrust, hence thedifferent diameters.

After performing a vertical takeoff, the multicopter rotates the fronttiltwing (406) and back tiltwing (402) forward (not shown here) so thatall of the propellers are rotating about a longitudinal axis of rotationinstead of a vertical axis of rotation. This position or configurationis sometimes referred to herein as a forward flight position orconfiguration. In addition to rotating the tiltwings down and/orforward, the foldable inner propellers (408) are folded up (e.g., whenthe aircraft is in a stable state and it is safe to stop and stow thosepropellers). The thrust from these propellers (408) is not needed in theforward flight position, and so those propellers are turned off toconserve power and/or increase range. To reduce drag, those propellers(408) are folded up so that the blades are tucked into and/or along theside of their respective pylons.

First, some figures showing the exemplary multicopter in the forwardflight position are described below. Then, a sequence showing an exampletransition from vertical takeoff and landing to forward flight(including the rotation of the tiltwings and the stowing of the foldablepropellers) is described.

FIG. 5 is a diagram showing an elevated view of an embodiment of amulticopter with its tiltwings in a position for forward flight. In thisexample, the front tiltwing (500) and back tiltwing (502) have rotateddownward and/or forward so that the propellers are rotating about alongitudinal axis of rotation instead of a vertical axis of rotation.Returning briefly to FIG. 3, it is shown there that the front tiltwingincludes a cutout (310). In FIG. 5, that cutout permits the fronttiltwing (500) and the top of the fuselage (504) to fit together whenthe front tiltwing is in the forward flight position as shown here. Itis noted that the front part of the vertical stabilizers (506) is formedby or comes from the front tiltwing (500) and the back portion of thevertical stabilizers (508) is formed by or comes from the top of thefuselage (504). This design choice to split up the vertical stabilizerswas made because allows an airfoil shape in cruise but with a sturdierstructure than a single airfoil.

When flying in this forward flight position, it is not necessary for allof the propellers to be on. As such, the foldable inner propellers (510)are turned off at an appropriate time and/or when it is safe to do so.The non-foldable outer propellers (512) and the non-foldable backpropellers (514). It is noted that the propellers which are kept on(i.e., propellers 512 and 514) are the outermost propellers (i.e., theones at the corners) which give the multicopter the mostmaneuverability.

The following figure shows a corresponding side view.

FIG. 6 is a diagram showing a side view of an embodiment of amulticopter with its tiltwings in a position for forward flight. Whenflying in this mode, the position of the front tiltwing lift vector(600) and back tiltwing lift vector (602) depends upon where theaerodynamic lift forces act on the respective wings, which in turn isdetermined by the shape of the respective wing. In this position, thecenter of mass (604) is slightly forward relative to the front tiltwinglift vector (600).

The following figure shows a corresponding front view.

FIG. 7 is a diagram illustrating a front view of an embodiment of amulticopter with its tiltwings in a position for forward flight. As thisview shows, the non-foldable outer propellers (700), which are attachedto the front tiltwing (702), are rotating, as are the non-foldable backpropellers (704), which are attached to the back tiltwing (706). Thefoldable inner propellers (708) are stowed away and are shown with adotted circle to make them more visible.

The following figure shows a corresponding top view.

FIG. 8 is a diagram illustrating a top view of an embodiment of amulticopter with its tiltwings in a position for forward flight. Asbefore, the non-foldable outer propellers (800), which are attached tothe front tiltwing (802), are open, as are the non-foldable backpropellers (804), which are attached to the back tiltwing (806). Thefoldable inner propellers (808) are folded away.

The following figure shows an example of how the exemplary multicoptertransitions from vertical takeoff (e.g., where the tiltwings andpropellers are in the positions shown in FIGS. 1-4) to forward flight(e.g., where the tiltwings and propellers are in the position shown inFIGS. 5-8).

FIG. 9 is a diagram illustrating an embodiment of a transition fromvertical takeoff to forward flight. In the example shown, themulticopter is on the ground in position 900. Although not shown in thisfigure, other multicopter embodiments may include any appropriatelanding gear as desired (e.g., wheels, floats, skids, etc.). From theon-the-ground position (900), the multicopter ascends vertically as itperforms a vertical takeoff and ascends vertically to position 902. Forexample, the pilot may wish to ascend to some desired and/or recommendedaltitude before attempting the transition to forward flight so that themulticopter is in no danger of colliding with objects at lower altitudesduring the transition (e.g., power lines, buildings, trees, etc.).

From position 902, the multicopter pitches forward from a level positionand gets into pitched position 904. It is noted that during thetransition from level position 902 to pitched position 904, both thefront tiltwing and the back tiltwing are still in the vertical takeoffand landing position. That is, they have not yet begun to rotate intothe forward flight position at this time. In this example, the pitchangle of the multicopter at position 902 is approximately 20°. As shownhere, the multicopter is also ascending (i.e., moving upward vertically)as well as moving forward as it begins to pitch forward from position902 to position 904.

From pitched position 904, the front tiltwing and back tiltwing begin torotate down and forward into the forward flight position. See, forexample, position 906, where both the front tiltwing and back tiltwinghave partially completed their rotation from the vertical takeoff andlanding position (see, e.g., FIGS. 1-4) to the forward flight position(see, e.g., FIGS. 5-8) and are shown halfway between those twopositions. The multicopter also continues to ascend and also continuesto move forward during this transition from pitched position 904 topartially-rotated position 906.

The multicopter continues to rotate the front tiltwing and back tiltwingforward and downward until the tiltwings are completely in the forwardflight position, while the multicopter is tilted forward. In general,all transitional positions have the wings orientated in a way such thatthey are at the climb or descent angle that is desired. The wings areroughly level to the flow while the fuselage may be level or tilted down(possibly substantially). Once the tiltwings have completed theirrotation, the multicopter levels off. See, for example, position 908where the front tiltwing and back tiltwing are in the forward flightposition and the multicopter is level.

The multicopter then stops and stows the foldable inner propellers, asshown in 910. Note, for example, that the front tiltwing in position 908has two sets of propellers visible, whereas the front tiltwing inposition 910 only has a single set of propellers visible.

This transition is described more generally and/or formally in theflowchart below.

FIG. 10 is a flowchart of a transitional process from a vertical takeoffand landing position to a forward flight position. In some embodiments,the process is performed at least partially automatically by a flightcontroller. For example, making the transition from a vertical takeoffand landing position to a forward flight position may be difficult foran inexperienced pilot to do. For safety and ease of use, an aircraftmay be able to perform the transition automatically once instructed todo so by the pilot and/or passenger.

At 1000, a vertical takeoff is performed during which a front tiltwing,which includes two non-foldable outer propellers and four foldable innerpropellers, is held in a vertical takeoff and landing position; a backtiltwing, which includes two non-foldable back propellers, is held inthe vertical takeoff and landing position; and the four foldable innerpropellers are rotating. See, for example, positions 900 and 902 in FIG.9.

At 1002, the aircraft is pitched forward. See, for example, position 904in FIG. 9.

At 1004, the front tiltwing and the back tiltwing are rotated from thevertical takeoff and landing position to a forward flight position. See,for example, positions 906 and 908 in FIG. 9 and note how the tiltwingsswing down and forward.

At 1006, the aircraft is leveled. See, for example, the transition fromposition 906 (where the aircraft is pitched forward) to position 908(where the aircraft is level) in FIG. 9.

At 1008, the four foldable inner propellers are stowed. See, forexample, the transition from position 908 (where the foldable innerpropellers are rotating) to position 910 (where the foldable innerpropellers are stowed) in FIG. 9.

Returning briefly to FIG. 9, a similar transition occurs when theaircraft lands and the transition from forward flight position tovertical takeoff and landing position is made. The aircraft wouldgenerally fly forward and descend and the sequence of positions wouldfollow the reverse sequence: 910→ . . . →900. For brevity, that reversesequence of positions is not shown and/or described in great detailhere. The following flowchart does, however, describe such a process.

FIG. 11 is a flowchart of a transitional process from a forward flightposition to a vertical takeoff and landing position. In someembodiments, the process is performed at least partially automaticallyby a flight controller.

At 1100, four foldable inner propellers are opened and rotated duringwhich a front tiltwing, which includes two non-foldable outer propellersand the four foldable inner propellers, is held in a forward flightposition; and a back tiltwing, which includes two non-foldable backpropellers, is held in the forward flight position. For example, thiswould correspond to a transition from position 910 to 908 in FIG. 9. Theaircraft would be flying forward at a relatively constant altitude(i.e., the aircraft has not yet started descending).

At 1102, the aircraft is pitched forward. For example, the aircraftwould begin to descend and the aircraft would be pitched forward. Thefront tiltwings and the back tiltwings would still be held in theforward flight position and would have not yet started their rotation.

At 1104, the front tiltwing and the back tiltwing are rotated from theforward flight position to a vertical takeoff and landing position. See,for example, the transition from position 906 (where the tiltwings arecaught mid-rotation) to position 904 (where the tiltwings have completedtheir rotation into the vertical takeoff and landing position) in FIG.9. Generally speaking, the aircraft is flying forward and descendingduring this time.

At 1106, the aircraft is leveled. See, for example, position 902 wherethe aircraft is no longer tilted forward.

At 1108, a vertical landing is performed. See, for example, thetransition from hovering position 902 to on-the-ground position 900.

The following figure shows an example of a component to switch thetiltwings between the vertical takeoff and landing position and theforward flight position.

FIG. 12A is a diagram illustrating an embodiment of actuation cylinderswhich are used to rotate the front tiltwing and back tiltwing where thetiltwings are in a vertical takeoff and landing position. For clarity,some pylons and propellers are not shown because they would obstruct theobjects of interest (e.g., actuation cylinders, their connection points,the hinges, etc.).

In this example, the front actuation cylinder (1202 a/1202 b) is used torotate the front tiltwing and the back actuation cylinder (1204 a/1204b) is used to rotate the back tiltwing. In various embodiments, thesethe actuation cylinders may be pneumatic, hydraulic, or electricactuators. Each actuation cylinder is connected to a fixed point on theaircraft. For example, the front actuation cylinder (1202 a/1202 b) isconnected to a front fixed connection point (1206 a/1206 b) and the backactuation cylinder (1204 a/1204 b) is connected to back fixed connectionpoint (1208 a/1208 b). The other end of a given actuation cylinder isattached to the respective tiltwing being moved.

FIG. 12B is a diagram illustrating an embodiment of actuation cylinderswhich are used to rotate the front tiltwing and back tiltwing where thetiltwings are in a forward flight position. By extending or retracting aparticular actuation cylinder (e.g., front actuation cylinder 1202a/1202 b or back actuation cylinder 1204 a/1204 b), the correspondingtiltwing rotates about the corresponding hinge (e.g., front tiltwinghinge 1210 a/1210 b or back tiltwing hinge 1212 a/1212 b). For example,in FIG. 12A, the actuation cylinders are extended, which causes thetiltwings to point upwards so that the propellers rotate about avertical axis of rotation (i.e., the tiltwings are in the verticaltakeoff and landing position). In FIG. 12B, the actuation cylinders areretracted so that the tiltwings point forward so that the propellersrotate about a longitudinal axis of rotation (i.e., the tiltwings are inthe forward flight position).

Although only one actuation cylinder is shown per tiltwing from thisview, for redundancy (which is desirable in an aircraft), there may betwo or more actuation cylinders per tiltwing. This would enable thetiltwings still to be moved even if one of the actuation cylindersbecame inoperable.

The following figures describe various embodiments of foldablepropellers which may be used in the exemplary multicopter describedabove. In the first embodiment, the pylons are rectangular cuboids withrounded edges (e.g., with no cutouts for the blades of the propellers tofit into). In the second embodiment, the pylons have cutouts shaped tofit the blades so that when the blades are folded up and stowed away,the propeller is substantially cylindrical in shape which (further)reduces drag during forward flight.

FIG. 13A is a front-view diagram illustrating an embodiment of afoldable propeller with extended blades. In the example shown, theblades (1300 a) of the propeller are open and extended. The blades areconnected to the rest of the propeller via hinges 1302. The blades openand close passively and rotate freely about the hinges. When the rotoris spun up, centrifugal force causes the blades to (e.g., passively)open and extend, as shown in this figure. When the rotor is stopped, theblades fold in.

As seen from this view, the hinges are have a vertical offset (e.g.,they do not line up on the same horizontal line) which creates acorresponding vertical offset in the blades.

FIG. 13B is a front-view diagram illustrating an embodiment of afoldable propeller with folded blades. In this example, the blades (1300b) of the propeller are closed and folded. To put the blades into thisposition, the propeller is stopped. The multicopter is expected to beflying a forward flight mode during this time and the forward movement(e.g., and resulting wind resistance) will push the blades back (e.g.,from the plane of rotation) into a closed position. This passive openingand closing of the blades helps to reduce potential points of failureand keeps weight and complexity down. To open the blades (e.g., puttingthe propeller back into the position shown in FIG. 13A), the propellerswould be “spun up.”

FIG. 14A is a side-view diagram illustrating an embodiment of a foldablepropeller with extended blades. In this view, the pylon (1400) and fronttiltwing (1402) are more visible. The open blades (1404 a) are alsoshown, as is the hinge (1404).

FIG. 14B is a side-view diagram illustrating an embodiment of a foldablepropeller with folded blades. In this view, the blades (1404 b) arefolded. As shown here, the pylon (1400) is long enough so that the tipsof the folded blades (1404 b) do not come into contact with the leadingedge of the front tiltwing (1402) when the blades are folded.

FIG. 15A is a top-view diagram illustrating an embodiment of a foldablepropeller with extended blades. In this view, the blades (1500 a) areopen. The hinges (1502), pylon (1504), and front tiltwing (1506) arealso visible.

FIG. 15B is a top-view diagram illustrating an embodiment of a foldablepropeller with folded blades. In this view, the blades (1500 b) areclosed.

FIG. 16A is an angled-view diagram illustrating an embodiment of afoldable propeller with extended blades. In this view, the blades (1600a) are open. The hinges (1602), pylon (1604), and front tiltwing (1606)are also visible.

FIG. 16B is an angled-view diagram illustrating an embodiment of afoldable propeller with folded blades. In this view, the blades (1600 b)are closed.

FIG. 17A is a diagram illustrating an embodiment of foldable propellerwith open blades and a pylon shaped to fit the stowed blades. In thisview, the blades (1700 a) are open. The propeller also includes pylon1702 which has a concave portions (1704) that the blades fit into whenthey are closed or stowed. This concave portion may also be referred toas a concave depression or a cutout. In some embodiments, concavedepression (1704) may be shaped according to a corresponding blade'scurvature.

FIG. 17B is a diagram illustrating an embodiment of foldable propellerwith folded blades and a pylon shaped to fit the stowed blades. In theexample shown, blades 1700 b are folded and tucked into pylon 1702,specifically, cutout 1702. As shown, when folded, the exposed surface ofthe folded blades 1700 and the exposed surface of the pylon (1704)collectively form a smooth surface, specifically, a smooth convex shape.Although a teardrop shape is shown here, in some embodiments the pylonwith the folded blades forms some other shape (e.g., cylindrical,rectangular cuboids with rounded edges, etc.).

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. An aircraft, comprising: a fuselage whichincludes a windshield; a starboard-side non-foldable outer propeller; aport-side non-foldable outer propeller; a starboard-side foldable innerpropeller; a port-side foldable inner propeller; and a tiltwing,wherein: the tiltwing is a single common wing to which thestarboard-side non-foldable outer propeller, the port-side non-foldableouter propeller, the starboard-side foldable inner propeller, and theport-side foldable inner propeller are coupled to; the starboard-sidenon-foldable outer propeller, the port-side non-foldable outerpropeller, the starboard-side foldable inner propeller, and theport-side foldable inner propeller rotate at least some of the time whenthe tiltwing is in a vertical takeoff and landing position; thestarboard-side foldable inner propeller and the port-side foldable innerpropeller are stowed at least some of the time when the tiltwing is in aforward flight position; and the tiltwing is coupled to the fuselageabove and aft of the windshield and the tiltwing rotates about an axisof rotation, when rotating between the vertical takeoff and landingposition and the forward flight position, that is higher than theaircraft's center of mass.
 2. The aircraft recited in claim 1, wherein:the starboard-side foldable inner propeller and the port-side foldableinner propeller have a first diameter; the starboard-side non-foldableouter propeller and the port-side non-foldable outer propeller have asecond diameter; and the first diameter is larger than the seconddiameter.
 3. The aircraft recited in claim 1, wherein: thestarboard-side foldable inner propeller and the port-side foldable innerpropeller have a first diameter; the starboard-side non-foldable outerpropeller and the port-side non-foldable outer propeller have a seconddiameter; the first diameter is within a range of 1-1.5 meters; and thesecond diameter is within a range of 0.5-1 meters.
 4. The aircraftrecited in claim 1, wherein: the starboard-side foldable inner propellerand the port-side foldable inner propeller are connected to the tiltwingusing a first set of one or more pylons; the starboard-side non-foldableouter propeller and the port-side non-foldable outer propeller areconnected to the tiltwing using a second set of one or more pylons; andthe first set of one or more pylons are longer than the second set ofone or more pylons.
 5. A method, comprising: performing a verticaltakeoff of an aircraft during which a tiltwing of the aircraft is heldin a vertical takeoff and landing position, wherein: the tiltwing is asingle common wing to which a starboard-side non-foldable outerpropeller, a port-side non-foldable outer propeller, a starboard-sidefoldable inner propeller, and a port-side foldable inner propeller arecoupled to; and the starboard-side non-foldable outer propeller, theport-side non-foldable outer propeller, the starboard-side foldableinner propeller, and the port-side foldable inner propeller rotate atleast some of the time when the tiltwing is in the vertical takeoff andlanding position; after performing the vertical takeoff, rotating thetiltwing from the vertical takeoff and landing position into a forwardflight position, wherein the tiltwing is coupled to a fuselage above andaft of a windshield and the tiltwing rotates about an axis of rotation,when rotating between the vertical takeoff and landing position and theforward flight position, that is higher than the aircraft's center ofmass; and after rotating the tiltwing from the vertical takeoff andlanding position into the forward flight position, stowing thestarboard-side foldable inner propeller and the port-side foldable innerpropeller at least some of the time when the tiltwing is in the forwardflight position.
 6. The method recited in claim 5, wherein: thestarboard-side foldable inner propeller and the port-side foldable innerpropeller have a first diameter; the starboard-side non-foldable outerpropeller and the port-side non-foldable outer propeller have a seconddiameter; and the first diameter is larger than the second diameter. 7.The method recited in claim 5, wherein: the starboard-side foldableinner propeller and the port-side foldable inner propeller have a firstdiameter; the starboard-side non-foldable outer propeller and theport-side non-foldable outer propeller have a second diameter; the firstdiameter is within a range of 1-1.5 meters; and the second diameter iswithin a range of 0.5-1 meters.
 8. The method recited in claim 5,wherein: the starboard-side foldable inner propeller and the port-sidefoldable inner propeller are connected to the tiltwing using a first setof one or more pylons; the starboard-side non-foldable outer propellerand the port-side non-foldable outer propeller are connected to thetiltwing using a second set of one or more pylons; and the first set ofone or more pylons are longer than the second set of one or more pylons.9. A method, comprising: opening and rotating a starboard-side foldableinner propeller and a port-side foldable inner propeller in an aircraftwhile a tiltwing in the aircraft is held in a forward flight position,wherein: the tiltwing is a single common wing to which a starboard-sidenon-foldable outer propeller, a port-side non-foldable outer propeller,the starboard-side foldable inner propeller, and the port-side foldableinner propeller are coupled to; the starboard-side foldable innerpropeller and the port-side foldable inner propeller are stowed at leastsome of the time when the tiltwing is in a forward flight position;after opening and rotating the starboard-side foldable inner propellerand the port-side foldable inner propeller, rotating the tiltwing fromthe forward flight position into a vertical takeoff and landingposition, wherein the tiltwing is coupled to a fuselage above and aft ofa windshield and the tiltwing rotates about an axis of rotation, whenrotating between the vertical takeoff and landing position and theforward flight position, that is higher than the aircraft's center ofmass; and after rotating the tiltwing from the forward flight positioninto the vertical takeoff and landing position, performing the verticallanding of the aircraft, wherein the starboard-side non-foldable outerpropeller, the port-side non-foldable outer propeller, thestarboard-side foldable inner propeller, and the port-side foldableinner propeller rotate at least some of the time when the tiltwing is inthe vertical takeoff and landing position.
 10. The method recited inclaim 9, wherein: the starboard-side foldable inner propeller and theport-side foldable inner propeller have a first diameter; thestarboard-side non-foldable outer propeller and the port-sidenon-foldable outer propeller have a second diameter; and the firstdiameter is larger than the second diameter.
 11. The method recited inclaim 9, wherein: the starboard-side foldable inner propeller and theport-side foldable inner propeller have a first diameter; thestarboard-side non-foldable outer propeller and the port-sidenon-foldable outer propeller have a second diameter; the first diameteris within a range of 1-1.5 meters; and the second diameter is within arange of 0.5-1 meters.
 12. The method recited in claim 9, wherein: thestarboard-side foldable inner propeller and the port-side foldable innerpropeller are connected to the tiltwing using a first set of one or morepylons; the starboard-side non-foldable outer propeller and theport-side non-foldable outer propeller are connected to the tiltwingusing a second set of one or more pylons; and the first set of one ormore pylons are longer than the second set of one or more pylons.